A turbocompressor may be used, for example, in a plant in the chemical industry. In the plant there is normally a supply of thermal energy in the form of process steam. This process steam is made available in a process steam system, from which the process steam can be drawn off to drive a steam turbine. The steam turbine is usually used to drive the turbocompressor.
Normally, the turbocompressor is operated in various operating states, which can be associated with different rotation speeds of the turbocompressor. Usually, the rotation speed of the turbocompressor influences the drive power consumed by the turbocompressor, where the thermal power provided from the process steam system is usually greater than the power which is required to drive the turbocompressor. This surplus power increases as the power consumption of the turbocompressor reduces.
Usually, this excess power is not used, or it is fed into an additional turbine set which is installed in the plant and consists of a steam turbine and a generator.
FIG. 2 shows a steam turbine set having a generator 101 and a steam turbine 102. The steam turbine 102 drives the generator 101 via a first coupling 104. For the purpose of driving the steam turbine 102, live steam is fed in from a live steam line 106 to the steam turbine 102. The electrical power produced by the generator 101 is input into an electrical network 107.
In addition, the steam in the live steam line 106 is used to drive another steam turbine 108, which is in turn coupled via a coupling 105 to drive a turbocompressor 103. The rotation speed of the turbocompressor 103 is regulated by means of a rotation speed feedback device 109, which controls a live steam valve 108a. Thus when a predetermined rotation speed is specified for the turbocompressor 103, the live steam valve 108a is actuated by means of the rotation speed feedback device 109 in such a way that the quantity of steam fed from the live steam line 106 to the steam turbine 108 is set in such a way that the turbocompressor 103 is set and held at the predefined rotation speed.
For control and process engineering reasons, the steam turbine 108 which drives the turbocompressor 103 is designed to be overdimensioned. The steam turbine 108 must, for the minimum parameters of the live steam line 106, make available the maximum necessary drive power for the turbocompressor 103. Apart from this, the steam turbine 108 must enable the turbocompressor 103 to be run up even with reduced live steam parameters. For this reason, the steam turbine 108 is only subject to about 70% of the maximum steam throughput when operating as rated. A consequence of this is that the steam turbine 108 is run for most of its operating time with the live steam valve 108a throttled back. Because of this, the efficiency of the steam turbine 108 is far below its maximum efficiency.
The excess live steam which is available in the live steam line 106 is fed away by means of the steam turbine 102 and the generator 101. However, the additional provision of the steam turbine 102 and the generator 106 in the plant is demanding and costly.
FIG. 3 shows a conventional string, having a generator 101, a steam turbine 102 and a turbocompressor 103. The steam turbine 102 is fed with live steam from a live steam line 106 and for drive purposes is coupled to the generator 101 by means of a coupling 104, and to the turbocompressor 103 by means of a coupling 105.
The electrical power produced in the generator 101 is fed into an electrical network 107. The turbocompressor 103 is operated at a constant rotation speed.
For the reasons previously cited, at its rated load and partial load the steam turbine 102 is run throttled back, so that the efficiency of the steam turbine 102 also lies below its optimum efficiency. Further, there is no possibility of regulating the turbocompressor 103 by its rotation speed, which leads to a loss of efficiency for the entire process.